442 Proceedings of the Royal Irish Academy. 



and develops into an inflorescence or leaf -shoot. This mode of develop- 

 ment has led to an erroneous idea among gardeners, who very gene- 

 rally regard the lateralhranches as arising on the stem opposite the leaves. 

 At other positions round the hase of the internodes other swellings, 

 which are the beginnings of adventitious roots, are very usually 

 met with. These, as they develop, have also to pierce through the 

 petiole, and were it not for the difference in their position it would 

 he difficult to distinguish the branches just emerging, after piercing 

 the petiole, from roots in the same stage, so completely endogenous 

 do the former at first sight appear. The similarity between root and 

 shoot is increased by the fact that these aerial roots of Vanda teres 

 possess chlorophyll as is usual in the aerial roots of orchids. A 

 longitudinal section of a bud still enclosed by the axil (PL si., fig. 7) 

 shows that it is raised slightly above the axil, and its axis is perpen- 

 dicular to the main axis. The young leaves of the bud form domes 

 covering over the apex, which are only perforated by narrow slits, 

 inconspicuous even in sections cut at right angles to the axis of the 

 bud (PI. XL, fig. 3). The slight thickening on these domes, seen in 

 longitudinal section (PL xii., fig. 7), represent the lamina. The first 

 leaf of the lateral shoot is on its upper side. When such a bud as this 

 develops, the lamina of the lowest visible leaf, even when quite mature, 

 is only a small knob on the distal part of the petiole. Beneath this 

 leaf there are usually two leaves, which remain rudimentary, and 

 which are not evident except when seen in longitudinal section 

 (PL XIV., fig. 20). Sometimes the lowest visible leaf is only repre- 

 sented by a short tubular petiole, while the leaf next above it has a 

 knob-like lamina. During the development of a lateral bud, the cells 

 of the petiole of the subtending leaf, opposite the bud, lose their con- 

 tents and collapse. This phenomenon is not altogether due to the 

 pressure exerted by the developing bud, as it seems to take place 

 almost simultaneously on the outer and inner surfaces. The median 

 vascular bundle in the petiole was never found to be severed in this 

 penetration of the petiole, but merely pushed aside (PL xiv., fig. 28). 

 A comparison of the apical bud with a lateral bud shows us that 

 although both are constructed on the same plan, the parts of the 

 apical bud are more elongated. Also the thickenings on the domes, 

 representiug the laminae, in addition to beiag more elongated, are, in 

 their early stages, situated centrally over the apex, so that the 

 youngest visible leaf on the apex of a plant of Vanda teres appears, 

 having its base enveloped in the petiole of the next leaf, like a pro- 

 longation of the stem. Tracing, then, this leaf down into the petiole 



